My computer shutdown suddenly then i get Your project was created with an incompatable version of Unity

I use unity 4.6.8 : My computer shutdown suddenly when unity project was open, then when i try to open my unity project I get Your project was created with an incompatable version of Unity . my project opened when i pressed continue but the problem not solved . - I try to re-installing unity 4.6.8 but the problem not solved . -the problem not happen when i try to open another project . - I clicked reimport all but the problem not solved. - i I really did't open the project with another unity version So why this happen ?